This invention relates broadly to refrigeration systems, and more particularly to drive mechanisms for refrigeration systems of the type including two communicating cylindrical vessels having piston-like elements reciprocating therein.
Many refrigeration systems employ a working volume defined by two elongated cylindrical vessels having piston-type elements (displacers and/or pistons) slideably mounted therein making sealing contact with the inner walls thereof. In such systems, regenerators are normally coupled between ends of the working volume (which are also the ends of the cylindrical vessels) and intermediate portions of the working volume. Thus, when the piston-like elements are moved within the cylindrical vessels, refrigerant fluid is driven through the regenerators between the ends of the working volume and the intermediate portions. Refrigeration systems operating in both Stirling and Vuilleumier modes usually have such structures. In the case of Vuilleumier-cycle apparatus, one end of one of the elongated cylindrical vessels (one end of the working volume) is heated and cold is produced at an opposite end of the other elongated cylindrical vessel (the other end of the working volume). In the case of Stirling-cycle apparatus, one of the piston-like elements is a compression piston for producing pressure pulses in the working volume. In both cases, however, the piston-like elements are interconnected by linkages which move them within their respective vessels in appropriate phase relationships to produce cooling.
With regard to an appropriate phase relationship for producing cooling, it can be shown that approximately a 90.degree. phase relationship between an increase in pressure in the working volume and displacer movement from an area of the working volume to be cooled (and a similar phase relationship between a decrease in pressure and displacer movement toward the area to be cooled) will produce cooling at this area. In the case of Stirling-cycle apparatus, the pressure changes are achieved by the compressor piston. In the case of Vuillieumier-cycle apparatus, the pressure changes are achieved thermally by means of movement of a second displacer.
In the prior art, the piston-like elements have been driven by complex mechanisms, such as crank mechanisms disclosed in U.S. Pat. No. 3,862,546 to Daniels and U.S. Pat. No. 3,673,809 to Bamberg (FIGS. 10 and 11). Not only are such mechanisms expensive to manufacture and maintain, since they do not produce straight drives on rods or shafts entering sealed vessels, they cause wear on dynamic seals surrounding the shafts and tend to wear out these seals. Failure of these seals sometimes allows hot gases to by-pass heat exchangers and regenerators to reduce the efficiencies of such systems. Thus, it is an object of this invention to provide a refrigeration system which does not employ complex crank mechanisms for driving piston-like elements of refrigeration systems and which reduces wear on dynamic seals as compared to prior-art systems.
Similarly, it is an object of this invention to provide a linkage between two piston-like elements of a refrigeration system having a force acting substantially only axially, and not laterally, so as to not apply pressure on dynamic seals.
Another problem that exists in the prior art is that with most systems, such as the crank system described above, a driving force can be applied in only one direction for the system to operate. If a crank system is driven in reverse on most Stirling machines, for example, there will be produced a severe heating at the intended "cold end", resulting in rapid, self-destruction of the machine. The reason for this is that the phase relationship between volume and pressure will be reversed. Thus, it is yet another object of this invention to provide a refrigeration system having a linkage between piston-like elements to which energy can be applied in either direction and cooling will still be produced at the intended "cold end. "